Field of the Present Disclosure
The present disclosure relates to a method for analyzing an image of rod-shaped particles, and, more particularly, a method for analyzing an orientation distribution, length distribution and/or area fraction of rod-shaped particles from a black-white image of a network of the rod-shaped particles.
Discussion of Related Art
Recently, metal nano-wires have attracted attention as a next generation flexible transparent electrode. The performance of the transparent electrode film is determined from the network of nano-wires. For understanding the structure (connectivity, wire versus area ratio, orientation distribution, etc.), an image of the microscopic inner configuration of the nano-wires taken using films should be checked.
Multifunctional films (for example, transparent electrodes, molecular sieve membranes, etc.) made of nano-materials in material engineering or processes can be described in terms of electrical, optical and mechanical macroscopic properties. Although appropriate equipment (four-point probes, UV spectrometers, and uniaxial tensile testing machines) are used to locate such macroscopic properties, in fact, such macroscopic properties are closely related to the internal microscopic networks of the multifunctional films. Particularly, in networks composed of rod-shaped particles, the diameter, length distribution, number density, orientation, and connectivity of the rod-shaped particles are involved in these macroscopic properties. Therefore, measuring these microscopic properties can provide highly valuable information that allow the engineers to coordinate the networks to meet requirements for the desired physical, chemical, or electrical film.
Measuring these properties is especially important in the field of silver nano-wire transparent electrodes. In this connection, electrical properties are related to the percolation path of the current (related to the number and aspect ratio of the nano-wires). The optical properties are closely related to an area fraction referring to a ratio between a total area of a substrate and an area of the rod-shaped particles. To determine these microscopic characteristics, a high magnification image taken with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) should be used for the analysis. In this connection, using appropriate image analysis techniques, we will be able to understand the opto-electric properties of the mass-produced films in relation to their process conditions. For example, in dip coating, the speed of the substrate can control the number density of the nano-wires within the film, which affects the overall electrical properties of the film. Therefore, image analysis can be used to gather the information needed to design new process conditions or to design optimal process conditions to control microscopic structures within the film.
Recently, image analysis has been used as a major tool in many engineering fields. Many image analysis measurement techniques, such as transformation with watershed filtering, and Hough transform for circle, etc. have been proposed to detect circular particles. However, the technique of finding rod-shaped particles is rare. In this connection, a Hough transform is known as a method of finding rod or line-shaped particles, but it is very sensitive to parameter changes. In other words, this is not suitable for automated search of rod-shaped particles in complex networks because of the user's involvement. Another recently reported papers proposed a method for finding the orientation of various rod-shaped particles, but it was not a technique for analyzing the characteristics of individual rod-shaped particles.